Re-create a mirrored RAID after restoring backup

Question

As a follow-up on my thread http://discussions.apple.com/thread.jspa?threadID=833779&tstart=0 :
On a XServe G5 with OS X Server 10.4.8 and a two-drive mirrored RAID I do backups by cloning the RAID onto an other disk (in bay three) using Intego's Personal Backup X4.
Now it may happen that there is some kind of data loss or an other emergency case that urges me to boot from the cloned HD. I would do this by simply removing the HD in bay one and replacing it with the clone, then restart the server (second HD of the RAID1 remains in bay two).
The information I got until yet says that the mirrored RAID is then broken and needs to be completely re-build. Is this correct so far ? I originally assumed that the clone "remembers" that it was part of a RAID system before and rebuilds automatically with the second HD still in place. Very likely wrong ?
So if I need to rebuild the clone from scratch, which steps do I follow exactly ? As far as I understand I have two choices:
(1)
Via command line (as root): diskutil createRAID mirror <set name> Journaled HFS+ <device identifier disk1> <device identifier disk2>
<set name>: Would be volume name of the RAID to create, right ?
<device identifier disk1/2>: What is this and how to determine ?
(2)
Via disk utility: Select one disk (first line on the left disk/volume list, e.g. "76,2 GB Hitachi 123ABC"), click in "RAID" tab, do settings.
Then drag & drop each harddisk from the left to the right list (again, the first line of each disk entry). Finally creating the RAID by clicking at the button "Generate".
I'm not sure, although I would likely handle this with the disk utility, it appears easier to me using the diskutil command in terminal. But maybe I simply lack of explaining the GUI... let me know how to post images and I will add some screenshots here.
Well, if my proceedings are too complex and there is something easier, please let me know. I'm open for everything.

Answer 1

>This part of my question originally referred to the fact that when booting from the cloned backup in bay one while still having the second disk of the old RAID in bay two, it could occur that the OS rebuilds the RAID by using the data on the remaining mirror disk in bay two, couldn't ? This would be not desired, because the data on that disk would be no longer usable. So just for clarification, not that we have a misunderstanding in this point.
I see what you're getting at, and I don't believe it's an issue.
Given three disks, disk0, disk1 and disk2, where disk0 and disk1 are mirrored and that mirror fails, the OS will not rebuild the mirror using disk1 and any other disk. It won't arbitrarily choose any disk in the system to rebuild on - you have to specifically mark as disk as usable, either by enabling auto-rebuild and adding a spare disk to the array, or by using 'repairMirror' and specifying the disk to use.
In any case, if you reboot the system from disk2, there is no way it will rebuild the array using that disk since that disk is the active boot drive and can not be unmounted (which is necessary before being added to an array).
So, no, there is no chance that the system will auto-rebuild the working half of the mirror with your backup disk.
>Okay, let's summarize... I would follow this procedure in order to boot from the cloned backup and build a new RAID:
1. Remove both disks from the XServe.
2. Insert the cloned backup disk and boot.
3. Open terminal, su root, execute:
diskutil enableRAID disk0
diskutil repairMirror disk0 disk1
This is not correct.
When you 'enableRAID disk0' the OS will create a new, virtual disk (likely 'disk2'). This is the mirror array (currently consisting of only one drive), and it is this virtual disk that you need to specify as the mirror to be repaired.
So, given disk0 and disk1 as being the physical disks in the server, the steps are more likely to be:
<pre class=command>diskutil enableRAID disk0</pre>
(this creates a new, virtual disk2)
<pre class=command>diskutil repairMirror disk2 disk1</pre>
(this adds physical disk1 to the degraded mirror disk2)
When complete disk2 will be a mirror RAID consisting of disk0 and disk1.
>When using "diskutil enableRAID", I cannot determine the label of the RAID as I would do with "diskutil createRAID" (in command line manual this is referred to "setname"). Which setname does my "new" RAID system get, a default one ?
You know, I have no idea
I've never noticed this before. If I think about it, I'd guess that the setname is based on the source disk name.
>> If you add a drive to a RAID it gets reformatted, so it doesn't matter what's
on it.
Even if it was part of the RAID system before (the original disk in bay two) ? It could still have the RAID information on it and try to rebuild RAID when getting mounted, couldn't ?
No. See my comments above. The OS won't auto-rebuild unless a) the RAID is set to auto-rebuild and b) there is a spare disk in the array. If either of those two conditions are not true then the disk acts as a degraded mirror and can be reformatted/reallocated as you like.